XLib: XSetInputFocus not working, how to fix?

Question

linux

I'm writing a (justforfun) window manager.
When a new window is created (i.e. on a ConfigureRequest), the following is done:

//... (В классе окна)

    XWindowChanges  changes;                                                                                                                                                               
    changes.x = e->x;                                                                                                                                                                      
    changes.y = e->y;                                                                                                                                                                      
    changes.width = e->width;                                                                                                                                                              
    changes.height = e->height;                                                                                                                                                            
    changes.border_width = e->border_width;                                                                                                                                                
    changes.sibling = e->above;                                                                                                                                                            
    changes.stack_mode = e->detail;                                                                                                                                                        
    XConfigureWindow(display, this->window, e->value_mask, &changes); 

    //... (В классе самого оконного менеджера)

    XRaiseWindow(this->display, tw->get_xwindow());                                                                                                                                        
    XSetInputFocus(this->display, tw->get_xwindow(), RevertToPointerRoot, CurrentTime);

But the focus is still given to the window under the cursor.
How to make focus only on one (specified) window?